Voltage indicator



Jan. 2, 1945. F, ELSTON VOLTAGE INDICATOR Filed Aug 29, 1942 INVENTOR fiml /A w,

Patented Jan. 2, 1945 VOLTAGE mmcatron George F. Elston, Bloomfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application August 29, 1942, Serial No. 456,607

2 Claims.

My invention relates to voltage indicating devices, more particularly to electron discharge devices of the type having a fluorescent anode responsive to electron bombardment for visually indicating voltages.

An amplitude modulated radio signal is usually tuned in by manipulating the tuning circuit until a detector voltage is peaked" or becomes a maximum. The peaked voltage may be viewed on a conventional voltmeter or on the fluorescent anode of an electronic tuning indicator tube of the type described inthe patent to Roberts 2,175,700, October 10, 1939. When frequency modulated signals are received, however, two voltages of opposite polarity must be compared and the tuning adjusted until the two voltages are equal. Unfortunately, these two voltages are also equal at or near zero when no signal is present, so the indicating device for comparing the voltages may indicate a signal is tuned-in while in fact there is no signal present. Further, voltage measurements are subject to error when the operator must visually compare the amplitude of two voltages. separately indicated in two different viewing areas.

An object of m invention is an improved voltage indicator for visually comparing two voltages in one viewing area.

Another object of my invention is a voltage indicator adapted for indicating frequency modulated signals.

Still another object of my invention is a voltage indicator for indicating absolute as well as relative values of two voltages.

The characteristic features of my invention are defined in the appended claims and one embodiment thereof is described in the following specification and shown in the accompanying drawing in which:

Figure 1 is a partly sectioned perspective view of a cathode ray indicator tube embodying my invention;

Figure 2 .is an end view of the device shown in Figure 1;

Figure 3 shows one circuit that may be connected to my improved indicator tube; and

Figures 4, 5, 6 and '7 show, respectively, the shaded and illuminated areas of the viewing surface of my improved indicator tube with various combinations of unknown voltages applied to the the anode may be covered with any material,".-

fleeting electrodes which, when operated at a negative voltage with respect to the anode, de-

flect electrons from a portion of the anode and in effect cast a pie-shaped shadow on the otherwise illuminated surface of the anode.

According to one embodiment of my invention the deflecting electrodes comprise two side-byside rods or ribbons of metal, between which a narrow flat beam of electrons may pass to the anode to create a line or pencil of light extending radially across the pie-shaped shadow area on the anode. As more fully hereinafter described, the relative potentials on the two deflecting electrodes determine the position of the light line between the boundaries of the shadow area. When the two deflecting electrodes are connected to two voltages to be compared, such as the two discriminator voltages of frequency modulated s gnals, centering of the light line in the pie-shaped shadow area indicates that the two voltages are equal. When the light is displaced on either side of its center position, unequal voltages are indicated, and when these voltages are of frequency modulated signals; detuning is shown.

In Figure 1 the anode or target I iswdishshaped and is coaxial with an indirectly heated oxide coated cathode 2. The interior surface of such as willemite, that glows or fluoresces when activated by bombarding electrons. In the particular tube shown in Figure 1 shadow producing electrodes 3 and 4 comprise flattened metal rods or ribbons insulatingly mounted sideby-side and in close spaced relation to the oathode. Electrodes 3 and 4 are provided with individual lead-in conductors. The rods 3 and 4 are preferably mounted with their flat sides opposed and with their edges toward the cathode. Conveniently, each rod may extend downwardly through the mica disc support I, and, with two bent leg portions 5 and 6, be attached to the underside of the mica and connected to their leadin conductors. From'the mica support each rod extends upwardly to a plane near the upper end the observer from the end of the cathode, a dish,- shaped shield 9, mounted on support rods I0,- ma be placed over the ends of the cathode and deflecting electrodes.

In Figure 3 the electrodes of my indicator tube are shown diagrammatically with connections for applying voltages from the detector or discriminator circuit of a receiver for frequency modue lated signals. The two voltages from the discriminator are of opposite phase and are applied, re-

spectively, to the anodes of the two diodes and 2|, the cathodes of the diodes being connected through two equal series connected resistors 22 and 23. The inner ends of the resistors are grounded at 24. Alternating current voltages applied to the diodes hence produce direct current voltages at opposite ends of the resistors 22 and 23. Through coupling resistors these two direct current voltages are applied to the grids of direct current amplifiers and 2B, the cathodes of which are connected together and are grounded through a cathode biasing resistor 21. Ampliflers 25 and 26 may be of the triode types as shown or of the multi-grid type. The anodes of the amplifier are directly coupled across resistors 28 and 29 to the deflecting electrodes 3 and l oi the indicator tube.

The value of resistor 21 and other circuit constants may be so adjusted that with no signal, the potentials of the deflecting electrodes 3 and 4 are equal to or near the voltage of the anode so that no shadow is cast by the deflecting electrodes. This would require zero or small values of current through the amplifiers and their resistors 28 and 29. The entire anode is then illuminated as suggested in Figure 4. It, now, tunedin signal voltages of opposite phase are applied to the two diode anodes from the discriminator circuit, the two amplifier grids change to a more positive potential, thus increasing the space current through the amplifiers and through the resistors 28 and 29 which in turn decreases the anode voltages of the amplifiers. The reduced anode voltages are accomplished by corresponding reduced deflecting electrode voltages. Voltages on the deflecting electrodes lower than the voltage of the anode I, repel or deflect the electrons normally travelling in all radial directions from the cathode and hence appear to cast an enlarged shadow on the fluorescent anode. when the two deflecting electrode potentials are equal and slightly negative with respect to the fluorescent anode, a line or pencil of light bisects the shadow area as shown in Figure 5. Hence, when two equal discriminator voltages are applied, the center position or the light line indicates correct tuning. If the two deflecting electrodes are not equal. as when the frequency modulated signals are detuned on either side or resonance, the light line will swing to either side of center as shown in Figures 6 or 7. Since the observer sees one viewing area only, equal deflecting electrode voltages are easily observed. The outer boundaries of the shadow area move-but little with variations over a considerable range in the voltage of the deflecting electrodes. whereas the position of the light line i quite sensitive to differential voltages of the deflecting electrodes.

In a tuning indicator tube constructed according to my invention and connected as shown in Figure 3. a shadow angle of nearly 90 is obtained for voltage ranging between 3 and 50 across each of the resistors 22 and 23 when the resistors values are approximately of the value indicated in Figure 3 and when the diodes 20 and 2| are of the type commercially known as 6H6 and the amplifiers 25 and 26 are of the type commercially known as the 6SL6GT. and when the voltage applied to the electrode I is 250 volts. The anode and cathode of the indicator tube has approximately the dimensions of the indicator tube commercially known as the 6.,AF6G, the two deflecting electrodes being .005 inch thick, .060 inch aaeasao wide, .040 to .090 inch apart, and about .040 inch from the cathode, which is .035 inch in diameter. The sensitivity of the light line to deflection depends, of course, on the cathode-to-deflecting electrode spacing as in the cathode ray tube.

My improved indicator tube may be employed in any circuit where two voltages are to be compared or their absolute or relative values determined. My device may be eflectively used for null indications or for balancing voltages and currents. The normal no-voltage or no-signal condition of a shadow area may be chosen so that the maximum shadow is seen with no voltage and so that the shadow boundary approaches the center as the voltage is applied. For example, the anode-cathode connection or diodes 20 and 2| may be reversed so that applied alternating cur-- rent signals will produce negative voltages with respect to ground at the outer ends of resistors 22 and 23 and so that the deflecting electrode voltage will decrease.

Scale marks or other indicia on the anode l to show the position or the light beam, are not necessary because the boundaries of the shadow area automatically fix the ends 01' a scale between which the line of light may move. This obviates the dimcult task in manufacture of mechanically orienting the deflection electrodes with respect to the anode. While deflecting electrodes 3 and l are equal distances from the cathode, equal negative voltages on the electrodes will always be indicated by precisely centered light line. If desired, the two deflecting electrodes 3 and 4 may be mounted end-to-end and parallel with the cathode opposite the luminous portion of the anode I. Unequal voltages on the deflecting electrodes, then, would be evidenced by shadow area boundaries with a distinct step or offset, and equal voltages would be evidenced by straight radial lines.

My improved voltage indicator Visually compares two voltages in one viewing area, indicates the absolute as well as the relative values of the two voltages. My indicator is easy to construct and is easy and accurate to operate.

I claim:

1. An indicator tube comprising a cathode and an annular anode having an extended surface, said surface being coated with a material which fluoresces when bombarded with electrons from said cathode, two parallel slat electron deflecting electrodes about twice the width of said cathode edge on to said cathode and between one side of the cathode and the anode, the inner edges of said electrodes being spaced from said cathode a distance about the diameter of said cathode and the region of influence of the deflecting fleld of one electrode being within the region of influence of the deflecting field of the other electrode.

2. A cathode, a dish-shaped anode coaxial with he cathode, fluorescent anode on the portion of the material facing the cathode, two side-by-side closely spaced metal slat deflecting electrodes edgeon to said cathode between the cathode and said portion of the anode with their inner edges spaced from said cathode a distance about the diameter of the cathode and adapted to cast two side-by-side shadows on said portion with a narrow line of light between the shadows, and a lead-in conductor for each of said deflecting electrodes.

GEORGE F. ELSTON. 

